The present invention relates to a method and a device for processing video pictures for display on a display device having at least two kinds of luminous elements with different time responses, a first kind of luminous elements having a first time response and a second kind of luminous elements having a second time response, wherein the first time response is slower than the second time response. Particularly, the present invention is related to the reduction of the phosphor lag artefacts caused by the different time responses of the luminous phosphor elements.
Though they are known for many years, plasma displays are encountering a growing interest from TV manufacturers. Indeed, this technology now makes it possible to achieve flat color panels of large size (out of the CRT limitations) and with very limited depth without any viewing angle constraints.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, the new Plasma technology has to provide a picture quality as good or better than the old standard TV technology. On the one hand, the Plasma technology gives the possibility of “unlimited” screen size, of attractive thickness, but on the other hand, it generates new kinds of artefacts, which could damage the picture quality. Most of these artefacts are different to those of known TV pictures and so more visible since people are used to seeing old TV artefacts unconsciously.
One of these artefacts is called the “phosphor lag” and is due to the different time responses of the luminous materials making the different colour components used in the panel. This difference generates a kind of yellowish trail behind and a blue area in front of the bright objects moving on a dark background mainly (or the opposite).
FIG. 1 shows the simulation of such a phosphor lag effect on a natural scene with a movement basically in the vertical direction, where the moving white trouser-leg in front of the black background generates such trail.
On a plasma panel, the red, green and blue luminous elements (also named phosphors while not necessarily having the chemical element P) do not have the same properties because of the chemical properties of each phosphor. In addition the life duration and the brightness are privileged at the expense of behaviour homogeneity. Measurements show that the green phosphor is the slowest, the blue one is the fastest and the red one is mostly in-between. Thus, behind a white object in motion, there is a yellow-green trail, and in front a blue area, as illustrated in FIG. 2. Since the red (R), green (G) and blue (B) cells have different response times, at the front and rear of a moving object like a white block, the concerning pixels are discolored.
In the future, the development of new chemical phosphor powders could avoid such problems by making the green and red phosphors quicker. Nevertheless, today it is not possible by signal processing only to completely suppress this effect but one can try to reduce it.
One known solution from the former patent application FR 0010922 of Thomson multimedia is to compensate the coloured trail while modifying the blue component in the temporal domain.
The most cumbersome on the phosphor lag effect is not the trail behind moving objects but its colour. Another solution is therefore to add a complementary trail on the color trail in order to discolor it or to add to the pixels in front of the moving object a complementary correction at least for the cells having the fastest response. These solutions are disclosed in another European Patent Application of the applicant EP 01250237.3.
These ideas applied together in a PDP give very good results, but need the implementation of a motion estimator.